1. Field of the Invention
The present invention relates to a method for producing an L-amino acid using a microorganism, and in particular, methods for producing an L-amino acid wherein the L-amino acid is L-glutamic acid, L-lysine, L-threonine, L-tryptophan or the like. These are industrially useful L-amino acids, for example, L-glutamic acid is useful as a seasoning, and L-lysine, L-threonine and L-tryptophan are useful as animal feed additives, health food ingredients, amino acid infusions, and so forth.
2. Brief Description of the Related Art
L-Amino acids are industrially produced by fermentation using various microorganisms. For example, L-glutamic acid is produced mainly by fermentation utilizing L-glutamic acid-producing bacteria of the so-called coryneform bacteria belonging to the genus Brevibacterium, Corynebacterium or Microbacterium, or mutant strains thereof (see, for example, Kunihiko Akashi et al., “Amino acid fermentation”, pp. 195-215, 1986, Japan Scientific Societies Press). As methods for producing L-glutamic acid by fermentation using other bacterial strains, methods of using a microorganism belonging to the genus Bacillus, Streptomyces, Penicillium or the like (refer to, for example, Japanese Patent Laid-open (KOKAI) No. 5-244970), methods of using a microorganism belonging to the genus Pseudomonas, Arthrobacter, Serratia, Candida or the like (refer to, for example, U.S. Pat. No. 3,563,857), methods of using a microorganism belonging to the genus Bacillus, Pseudomonas, Serratia, Aerobacter aerogenes (currently referred to as Enterobacter aerogenes) or the like (refer to, for example, Japanese Patent Publication (KOKOKU) No. 32-9393), methods of using a mutant strain of Escherichia coli (refer to, for example, Patent document 1), and so forth are known. In addition, methods for producing L-glutamic acid using a microorganism belonging to the genus Klebsiella, Erwinia, Pantoea or Enterobacter have also been disclosed (refer to, for example, U.S. Pat. No. 3,563,857, Japanese Patent Publication (KOKOKU) No. 32-9393, Japanese Patent Laid-open No. 2000-189175).
Such methods for producing target substances such as L-amino acids by fermentation using a microorganism as described above include methods of using a wild-type microorganism (wild-type strain), methods of using an auxotrophic strain derived from a wild-type strain, methods of using a metabolic regulation mutant strain derived from a wild-type strain as a strain resistant to one or more various drugs, methods of using a strain which is both an auxotrophic strain and metabolic regulation mutant strain, and so forth.
In recent years, recombinant DNA techniques have been used in the production of target substances by fermentation. For example, L-amino acid productivity of a microorganism can be improved by enhancing expression of a gene encoding an L-amino acid biosynthetic enzyme (U.S. Pat. Nos. 5,168,056 and 5,776,736), or by enhancing the inflow of a carbon source into an L-amino acid biosynthesis system (U.S. Pat. No. 5,906,925).
The kdp system functions as a P-type ATPase and works to take up potassium ions (Laimonis A. Laimins, Proc. Natl. Acad. Sci. USA, 1978 July, 75(7):3216-19). The kdp system is encoded by the kdp operon, and expression thereof is induced when the potassium ion concentration in a medium is low, or when the culture is performed under hyperosmotic conditions (Laimonis A. Laimins, Proc. Natl. Acad. Sci. USA, 1981 January, 78(1):464-68). Furthermore, it is known that the expression is controlled by KdpD and KdpE which constitute one of several binary control systems (Mark O. Walderhaug, J. Bacteriol., 1992 April, 174 (7):2152-59). However, the relationship between the enhancement of the kdp system and L-amino acid production has not been previously investigated.